Today is Trinity Sunday, a day which is notorious among clergy as one which preachers want to avoid. It is, I assure you, by accident and not design that the person speaking to you this evening is paid by the College to teach bizarre things such as Trinitarian theology to Worcester undergraduates. It is also a coincidence that some of those undergraduates begin their final examinations tomorrow. Any of them who have found their way into chapel this evening are far more likely to be placing their hopes in the power of prayer than in the power of my sermonising. And perhaps, a sermon is not the right medium anyway. The anthem we have just heard, Vaughan Williams’s setting of Herbert’s The Call is such an excellent example, both musically and poetically, of Trinitarian theology that it is tempting for me simply to sit down as invite the boys to sing it again. A friend of mine, who was for a long time a school chaplain, had a neat solution to the problem of teaching children this most difficult of theological ideas. He said, “I just tell them that it’s simple: three in one, and one in three. Any problems, go and ask your maths teacher.”

I’m going to try a slightly different approach. Picture the scene. A group of students gathers together, perhaps on a summer evening. Work is finished for the day, the sun is not long down, the wine is flowing. Idle chit chat puts the world to rights and all is as it should be. Except that two of the group are paying no attention to anybody else. You see, two of the group – as they will eagerly tell anyone prepared to listen – are very much in love, indeed have been very much in love for all of eight days – a practically matrimonial commitment in their eyes. And their time is spent not contributing, not participating but variously gazing into one another’s eyes, holding as much of the other’s hand as they can physically contain, and mostly, and all too prominently, snogging.

It is an experience almost all students are forced to endure at one time or another. It is a disease of the young, though not necessarily the young in years, since human behaviour tends to disobey the rules and regulations of chronology where matters of the heart are concerned. Many of us have been there. One of the worst fates in Oxford is to be stuck on the end of a long dining bench and table with only young lovers opposite. Conversation is hardly sparkling. I myself remember two friends from undergraduate days who, if separated by someone sitting between them, thought it acceptable to stretch out and hold hands across them. They were lucky that their neighbour didn’t respond by throwing up on their tightly clasped hands.

This is love, of a sort. And God, we are told, is love. So is such cringe making behaviour divine? Definitely not. It is no less a theologian than Rowan Williams who asks us to consider this kind of love, and try to map it on to the relationships which we call the Trinity. It will not work. The love of God is not entirely self-absorbed. The love of God is gratuitous, overflowing, it exceeds itself. When we say that God exists in a communion of love, we do not mean that the Father and the Son enjoy a relationship which is closed, in which they attend to nothing and no-one but each other. Instead their love has an openness, an outpouring which St Augustine of Hippo famously identified with the third person of the Trinity, with that which we call the Holy Spirit. In so doing, Augustine did not mean, as is often suggested, that Father and Son are rather like human persons, and that the Spirit is the abstract concept of love which flows between them. He meant that there are different ways in which scripture requires us to talk about God – as the source of all existence, as the divine presence which disrupts our tidy world of power at a particular time and in a particular place, and as the effect, the working out, the living out of that creativity and that presence in the world and in the lives of human beings such as you and I.

What follows from this is that everything that Christians do is done in the Spirit, done because of the life-giving presence of God which animates all creation. The Trinity, far from being the abstract concern of theological metaphysics, is actually the basis of the entire Christian life. Right at the beginning of Mark’s gospel, the first to be written, we see Father, Son and Spirit active in the baptism of Jesus, in the new act of creation by which everyone and everything will be reborn and renamed through the death and resurrection of Christ.

In the life of the church, the Trinity underlies everything which we call Christian. As I read scripture I do so seeking the God who sustains my existence in love, who himself seeks and sustains his people, and I am enabled to meet this God in the person of Jesus Christ precisely because the Spirit gives life to that scriptural encounter – without Father, Son and Spirit the Bible is simply another book. As I offer my prayers I do so knowing that the Father who loves his children sees not them in their sin but his son in their likeness, and so united with Christ I am able to pray, except that it is not I who prays but the Spirit who prays within me. The initiative here is grace itself: the love of the Father, in offering his Son in our likeness; the love of the Son in giving himself freely to the Father as our representative; the overflowing love of the Spirit which allows this relationship between Father and Son to spill out into the lives of every created thing.

Genuine love, divine love, is genuinely gratuitous. It is not simply selfless, in that it gives itself entirely to another; it is also endless, in that it cannot be exhausted by any single object of love, even an object as infinitely loveable as the person of Jesus Christ. When we struggle with the world in which we find ourselves, with the decisions, the relationships, the problems, the examinations, which make up our own little parts of that world, we are nonetheless living the life of the Spirit if we try, if only we try, to be loving. An act of love is an act of God, and the true act of God, the true act of love, is something which our own failures and weaknesses and selfishness can never diminish, however much they may knock us back, however determined we are to wallow in our own inadequacy. Divine love is not packaged up, a possession shared by Father and Son but kept to themselves and given to no-one else. It is an eternal act of self-giving which cannot end because the Spirit is always at work bringing life, bringing love, to every creature and person under heaven. The doctrine of the Trinity is the teaching that in the life of God himself there is something which overflows all attempts to contain it, there is an invitation for you and for me, a reminder that giving and sharing can be one and the same.